Reheat boiler

ABSTRACT

Provided is a reheat boiler in which the imbalance in temperature distribution of the temperature of the combustion gas at the outlet of a reheat furnace is reduced by changing the gas flow pattern in the reheat burner. A reheat boiler includes a main boiler configured such that main combustion gas generated in combustion in a burner flows from a furnace through a superheater and evaporator tubes, a reheat furnace that is disposed on the downstream of the evaporator tubes and produces reheat combustion gas by combustion in a reheat burner, and a reheater disposed above the reheat furnace. A closing plate, serving as a drift preventing portion, is provided at a reheat furnace outlet that connects the reheat furnace and the reheater to form a flow path for the combustion gas and the reheat combustion gas so as to narrow the cross-sectional area of the flow path for the combustion gas.

TECHNICAL FIELD

The present invention relates to a reheat boiler having a reheat furnace and a reheater on the downstream of evaporator tubes, in which an imbalance in temperature of the combustion gas near the outlet of the reheat furnace is reduced.

BACKGROUND ART

Conventionally, boilers having a superheater are employed as marine boilers (see Patent Literature 1).

Furthermore, conventional marine boilers use a reheat boiler having a reheat furnace and a reheater on the downstream of combustion gas.

FIG. 5 shows an example of the configuration of a conventional marine reheat boiler.

FIG. 5 is a schematic diagram showing the configuration of the conventional reheat boiler in a simple form. As shown in FIG. 5, a conventional reheat boiler 100 includes a main boiler 106 consisting of a burner 101, a furnace 102, a front tube bank 103, a superheater (superheater: SH) 104, and evaporator tubes (a rear tube bank) 105; a reheat furnace 108 having a reheat burner 107; and a reheater 109 provided on the exhaust-gas outlet side, the reheat furnace 108 and the reheater 109 being disposed on the downstream of the evaporator tubes 105.

The combustion gas generated by combustion in the burner 101 flows from the furnace 102 through the front tube bank 103, the superheater 104, and the evaporator tubes 105 to the reheat furnace 108, where it is mixed with the reheat combustion gas from the reheat burner 107, after which the combustion gas then flows while undergoing heat exchange with the reheater 109 and is discharged from a gas outlet 110, which has achieved efficient operation.

In FIG. 5, the reference numeral 111 denotes a water drum, 112 denotes a steam drum, 113 and 114 denote headers, and 115 denotes a wall tube.

CITATION LIST Patent Literature {PTL 1}

-   Japanese Unexamined Patent Application, Publication No. 2002-243106

SUMMARY OF INVENTION Technical Problem

In the conventional marine reheat boiler 100, the reheat burner 107 is installed only at the front wall of the reheat furnace 108, not at the rear wall of the reheat furnace 108.

Therefore, for example, as shown in FIG. 6, at the outlet of the reheat furnace 108 (a portion denoted by reference numeral B in FIG. 5), the difference in temperature of the combustion gas between the front wall (X in FIG. 6) side and the rear wall (Y in FIG. 6) side of the reheat furnace 108 is sometimes several hundred degrees. This significant imbalance in the temperature of the combustion gas is a problem. Such an imbalance in temperature of the combustion gas is considered to be due to incomplete mixing of the combustion gas and the reheat combustion gas because of a temperature difference between the combustion gas flowing from the main boiler 106 and the reheat combustion gas from the reheat burner 107.

The imbalance in temperature of the combustion gas at the outlet of the reheat furnace 108 (at the inlet of the reheater 109), i.e., the imbalance in the temperature distribution of the mixed combustion gas composed of the combustion gas and the reheat combustion gas, is undesirable because it may decrease the heat-transfer performance of the reheat furnace 108 and the reheater 109 and may lead to high-temperature corrosion of a reheat tube of the reheater 109 and a decrease in strength of a support member.

The present invention has been made in view of the above-described problem, and an object thereof is to provide a reheat boiler in which the imbalance in the temperature distribution of the combustion gas at the outlet of the reheat furnace is reduced by changing the flow pattern of the gas in the reheat burner.

Solution to Problem

To solve the above-described problem, the present invention employs the following solutions.

A reheat boiler according to an aspect of the present invention includes a main boiler configured such that main combustion gas generated by combustion in a burner flows from a furnace through a superheater and evaporator tubes, a reheat furnace that is disposed on the downstream of the evaporator tubes and produces reheat combustion gas by combustion in a reheat burner, and a reheater disposed above the reheat furnace. A drift preventing portion that narrows the cross-sectional area of a flow path for the combustion gas is provided at a reheat furnace outlet connecting the reheat furnace and the reheater and forming the flow path for the combustion gas and the reheat combustion gas.

In the reheat boiler according to the aspect of the present invention, the drift preventing portion that narrows the cross-sectional area of the flow path for the combustion gas is provided at a reheat furnace outlet connecting the reheat furnace and the reheater and forming the flow path for the mixed combustion gas (the combustion gas and the reheat combustion gas). This allows the flow of the main combustion gas and the reheat combustion gas passing through the drift preventing portion to cause turbulence, facilitating mixing.

In the above-described aspect, it is preferable that the drift preventing portion should be formed by attaching a closing plate to the outlet of the reheat furnace. This configuration enables the opening ratio of the cross-sectional area of the flow path to be easily adjusted by appropriately changing the size of the closing plate.

It is preferable that the closing plate in this case can be divided into a plurality of segments such that the segments can be independently attached or removed. This configuration enables the opening ratio of the cross-sectional area of the flow path to be easily adjusted at the installation site by changing the number of closing plate members attached or removed.

Advantageous Effects of Invention

In the above-described present invention, because the drift preventing portion that narrows the cross-sectional area of the flow path is provided at the outlet of the reheat furnace forming the flow path for the mixed combustion gas (the combustion gas and the reheat combustion gas), it is possible to allow the flow of the main combustion gas and the reheat combustion gas passing through the drift preventing portion to cause turbulence. Because this turbulence of the reheat combustion gas facilitates mixing of the combustion gas and the reheat combustion gas having different temperatures, it is possible to provide a reheat boiler in which the imbalance is reduced such that the temperature distribution of the mixed combustion gas is uniform at the outlet of the reheat furnace (at the inlet of the reheater) on the downstream side of the drift preventing portion.

In other words, because the flow pattern of the combustion gas and the reheat combustion gas can be changed by allowing the combustion gas and the reheat combustion gas to pass through the drift preventing portion, the two combustion gases having different temperatures are mixed on the downstream side of the drift preventing portion and flow in the reheater with a substantially uniform temperature distribution.

Thus, because the imbalance in temperature of the combustion gas at the inlet of the reheater is eliminated, heat exchange efficiently utilizing the entire area of the reheat furnace and reheater is possible. Therefore, it is possible to provide a high-efficiency reheat boiler in which a decrease in heat-transfer performance of the reheat furnace and the reheater is prevented or suppressed. In addition, by eliminating the imbalance in temperature of the combustion gas at the inlet of the reheater, high-temperature corrosion of the reheat tube of the reheater, as well as a decrease in strength of the support member due to the high temperature, can be prevented or suppressed. Thus, the durability and reliability of the reheat boiler can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram showing a reheat boiler according to an embodiment of the present invention.

FIG. 2A is a diagram showing an installation example of closing plates in FIG. 1, showing the case where a pair of closing plates are installed on the front and rear sides (on the left and right sides) of the cross-sectional area of the flow path.

FIG. 2B is a diagram showing an installation example of a closing plate in FIG. 1, showing the case where the closing plate is installed only on the front side (on the left side) of the cross-sectional area of the flow path.

FIG. 2C is a diagram showing an installation example of a closing plate in FIG. 1, showing the case where the closing plate is installed only on the rear side (on the right side) of the cross-sectional area of the flow path.

FIG. 3 is a graph showing the relationship between the opening ratio of the cross-sectional area of the flow path and the gas temperature ratio.

FIG. 4 is a perspective view of a relevant part showing a modification of the closing plate shown in FIG. 1.

FIG. 5 is a configuration diagram showing an example of the configuration of a conventional reheat boiler.

FIG. 6 is an explanatory diagram showing the temperature distribution of mixed combustion gas near the outlet of the reheat furnace.

DESCRIPTION OF EMBODIMENTS

A reheat boiler according to an embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 3.

Similarly to the reheat boiler 100 having the conventional structure shown in FIG. 5, a reheat boiler 10A according to this embodiment is configured such that the combustion gas generated by combustion in a burner 101 flows through a main boiler 106 in which the gas from a furnace 102 passes through a superheater 104 and evaporator tubes 105, a reheat furnace 108 in which the combustion gas is reheated in a reheat burner 107, and a reheater 109 through which the reheated combustion gas passes.

In the reheat boiler 10A having such a configuration, the combustion gas generated by combustion in the burner 101 flows from the furnace 102 and passes through the front tube bank 103, the superheater 104, and the evaporator tubes 105 in the main boiler 106. Then, the combustion gas flowing into the reheat furnace 108 from the main boiler 106 flows in the reheater 109 together with the reheat combustion gas generated in the reheat burner 107. Note that, in the following description, the gas composed of the mixture of the combustion gas flowing from the main boiler 106 and the reheat combustion gas generated in the reheat furnace 108, i.e., the gas flowing through the reheat furnace 108 and on the downstream thereof, is generally referred to as the “mixed combustion gas”.

The mixed combustion gas, which is the combustion gas flowing from the main boiler 106 merged with the reheat combustion gas generated in the reheat furnace 108, passes through a reheat furnace outlet (which is also the inlet of the reheater 109) 120 connecting the reheat furnace 108 and the reheater 109 and forming a flow path. The reheat furnace outlet 120 is provided with a closing plate 130 to form a drift preventing portion that narrows the cross-sectional area of the flow path for the mixed combustion gas.

This closing plate 130 narrows and drastically changes the cross-sectional area of the flow path at the reheater outlet 120, where the combustion gas flow flowing from the main boiler 106 and making a substantially 90-degree upward turn is merged with the reheat combustion gas flow rising from the lower side of the reheat furnace 108 and where the mixed combustion gas is directed from the reheat furnace 108 to the reheater 109. That is, the closing plate 130 installed in a high-temperature area where the high-temperature mixed combustion gas flows serves to narrow the cross-sectional area of the flow path for the mixed combustion gas at the reheater outlet 120 to temporarily and drastically reduce the cross-sectional area of the flow path.

Installation examples of the closing plate 130 that narrows the cross-sectional area of the flow path are shown in FIG. 2.

In the installation example shown in FIG. 2A, the closing plates 130 are attached on the front and rear sides (on the front wall side and the rear wall side), or on the left and right sides (on the left wall side and the right wall side), of the reheater outlet 120 to partially close the flow path and drastically reduce the cross-sectional area of the flow path.

In the installation examples shown in FIGS. 2B and 2C, the closing plate 130 is attached either on the front side or the rear side (on the front wall side or the rear wall side), or on the left side or the right side (on the left wall side or the right wall side), of the reheater outlet 120 to partially close the flow path and drastically reduce the cross-sectional area of the flow path.

The provision of this closing plate 130 drastically reduces the cross-sectional area of the flow path at the reheat furnace outlet 120 connecting the reheat furnace 108 and the reheater 109 and forming the flow path for the mixed combustion gas (the combustion gas and the reheat combustion gas), allowing the flow of the main combustion gas and the reheat combustion gas passing through the closing plate 130 to cause turbulence, such as swirl, such that they are stirred. That is, the flow of the combustion gas having made a substantially 90-degree upward turn and the flow of the reheat combustion gas rising upward collide with the closing plate 130, and a decrease in the cross-sectional area of the flow path changes the flow direction and increases the flow rate, making the flow pattern in the reheat furnace 108 complex. Thus, stirring and mixing of the combustion gas in the reheat furnace 108 is facilitated.

As a result, two flows of the mixed combustion gas having different temperatures are merged into a flow having a substantially uniform temperature as a whole by passing through the closing plate 130 and then flow in the reheater 109.

FIG. 3 is a graph showing the relationship between the opening ratio and the gas temperature ratio when the closing plate 130 is installed at the cross-sectional area of the reheater outlet 120.

In this graph, the opening ratio on the horizontal axis represents the proportion of the area of the opening where the cross-sectional area of the flow path of the reheater outlet 120 remains unclosed by the closing plate 130. The larger the value is, the greater the area of the opening serving as the flow path for the mixed combustion gas.

On the other hand, the gas temperature ratio on the vertical axis represents the ratio of the maximum gas temperature (Tmax) to the average gas temperature (Tav). The closer the value is to 1, the more uniform the temperature is. That is, as the gas temperature ratio increases, the difference between the maximum gas temperature and the average gas temperature of the mixed combustion gas increases, resulting in a greater temperature imbalance.

In FIG. 3, the smaller the opening ratio is, the closer the gas temperature ratio is to 1. Therefore, the larger the closing plate 130 installed to narrow the cross-sectional area of the flow path is, the more the stirring and mixing are facilitated, making the temperature of the mixed combustion gas uniform. However, although the imbalance in temperature of the mixed combustion gas is eliminated by reducing the opening ratio of the reheater outlet 120, the pressure loss occurring when the mixed combustion gas passes through the reheater outlet 120 having a reduced cross-sectional area of the flow path increases. Accordingly, the opening ratio of the reheater outlet 120 should be appropriately adjusted by changing the size of the closing plate 130 (the area of the flow path blocked) such that the maximum operating efficiency is achieved, taking into consideration the temperature imbalance and pressure loss of the mixed combustion gas. In other words, by employing the drift preventing portion formed by attaching the closing plate 130 to the reheat outlet opening 120, the opening ratio of the cross-sectional area of the flow path can be easily adjusted by changing the size of the closing plate 130.

Meanwhile, it is preferable that the above-described closing plate 130 should have a structure such that it is installed on stack tubes 140 extending through the reheat furnace outlet 120, like, for example, a closing plate 130A according to a modification of the above-described embodiment, shown in FIG. 4. The stack 140 is composed of evaporator tubes (stack) 141 crossing above the reheat furnace 108.

By employing this installation structure of the closing plate 130A, a new support member (projection member) does not need to be provided in the high-temperature area where the mixed combustion gas flows. Note that the support member mounted in the high-temperature area needs to be made of a high-quality material capable of withstanding a high-temperature environment.

Furthermore, the closing plate 130A shown in FIG. 4 is divided into a plurality of segments to enable the cross-sectional area of the flow path to be adjusted. In the configuration example shown, a pair of closing plates 130A on the left and right sides are each divided into three segments. That is, one closing plate 130A is divided into three, namely, closing plate members 131, 132, and 133, enabling the closing plate members 131, 132, and 133 to be independently attached or removed.

This configuration enables the opening ratio of the cross-sectional area of the flow path to be easily adjusted at the installation site by changing the number of closing plate members attached or removed. That is, the number of closing plate members 131, 132, and 133 to be installed can be easily adjusted by attaching or removing them to achieve the appropriate opening ratio on the basis of the result of a combustion test conducted on the reheat boiler 10A at the installation site (the temperature imbalance level, etc.). Note that the number of segments into which the closing plate 130A is divided is not limited to three as described above.

Furthermore, the closing plate 130A shown constitutes an inclined surface such that the area of the opening gradually increases toward the outlet. Therefore, the mixed combustion gas with a uniform temperature distribution is smoothly distributed in the reheater 109 and passes substantially uniformly through the entire interior of the reheater 109. Thus, the heat exchange efficiency in the reheater 109 is improved. Note that an improvement in the heat exchange efficiency in the reheater 109 is also effective in improving the efficiency of the reheat boiler 10A.

Thus, in the above-described reheat boiler 10A of the present invention, because the closing plate 130 that narrows the cross-sectional area of the flow path is attached to the reheat furnace outlet 120 constituting the flow path for the mixed combustion gas (the combustion gas and the reheat combustion gas) to form the drift preventing portion, the flow of the mixed combustion gas passing through the drift preventing portion causes turbulence, facilitating mixing. Thus, the temperature imbalance is reduced so that the temperature distribution is uniform at the outlet of the reheat furnace 108 (the inlet of the reheater 109) on the downstream side of the drift preventing portion. That is, because the flow pattern of the combustion gas and the reheat combustion gas, serving as the mixed combustion gas, can be changed by allowing the mixed combustion gas to pass through the drift preventing portion where the cross-sectional area of the flow path is narrowed by attaching the closing plate 130, the two combustion gases having different temperatures are mixed on the downstream side of the drift preventing portion and flow in the reheater 109 with a substantially uniform temperature distribution.

Accordingly, the imbalance in temperature of the mixed combustion gas at the inlet of the reheater 109 is eliminated, and it is possible to provide the reheat boiler 10A having a high efficiency in which a decrease in heat-transfer performance of the reheat furnace 108 and the reheater 109 is prevented or suppressed.

In addition, if the imbalance in temperature of the combustion gas at the inlet of the reheater 109 is eliminated, high-temperature corrosion of the reheat tube of the reheater 109 can be prevented or suppressed. Furthermore, if the imbalance in temperature of the combustion gas at the inlet of the reheater 109 is eliminated, a decrease in strength of the support member due to the high temperature can also be prevented or suppressed because the maximum gas temperature also decreases. As a result, the durability and reliability of the reheat boiler 10A are improved.

Note that the present invention is not limited to the above-described embodiment but may be appropriately modified within a scope not departing from the gist thereof.

REFERENCE SIGNS LIST

-   10A reheat boiler -   101 burner -   102 furnace -   103 front tube bank -   104 superheater (SH) -   105 evaporator tubes (rear tube bank) -   106 main boiler -   107 reheat burner -   108 reheat furnace -   109 reheater -   110 gas outlet -   111 water drum -   112 steam drum -   120 reheat furnace outlet -   130, 130A closing plate -   131, 132, 133 closing plate member -   140 stack tube -   141 evaporator tube (stack) 

1. A reheat boiler comprising: a main boiler configured such that main combustion gas generated by combustion in a burner flows from a furnace through a superheater and evaporator tubes; a reheat furnace that is disposed on the downstream of the evaporator tubes and produces reheat combustion gas by combustion in a reheat burner; and a reheater disposed above the reheat furnace, wherein a drift preventing portion that narrows the cross-sectional area of a flow path for the combustion gas is provided at a reheat furnace outlet connecting the reheat furnace and the reheater and forming the flow path for the combustion gas and the reheat combustion gas.
 2. The reheat boiler according to claim 1, wherein the drift preventing portion is formed by attaching a closing plate to the outlet of the reheat furnace.
 3. The reheat boiler according to claim 2, wherein the closing plate can be divided into a plurality of segments such that the segments can be independently attached or removed. 